1. Field
Embodiments of the present invention generally relate to a method for plasma etching extreme ultraviolet (EUV) material layers and, more specifically, to a method for etching an EUV anti-reflective coating (ARC) layer and absorber layer during photomask fabrication.
2. Description of the Related Art
In the manufacture of integrated circuits (IC), or chips, patterns representing different layers of the chip are created by a chip designer. A series of reusable masks, or photomasks, are created from these patterns in order to transfer the design of each chip layer onto a semiconductor substrate during the manufacturing process. Mask pattern generation systems use precision lasers or electron beams to image the design of each layer of the chip onto a respective mask. The masks are then used much like photographic negatives to transfer the circuit patterns for each layer onto a semiconductor substrate. These layers are built up using a sequence of processes and translate into the tiny transistors and electrical circuits that comprise each completed chip. Thus, any defects in the mask may be transferred to the chip, potentially adversely affecting performance. Defects that are severe enough may render the mask completely useless. Typically, a set of 15 to 30 masks is used to construct a chip and can be used repeatedly.
A photomask is typically a glass or a quartz substrate giving a film stack having multiple layers, including an ARC layer, an absorber layer and a capping layer disposed on other film materials, if any, thereon. When manufacturing the photomask layer, a photoresist layer is typically disposed on the film stack to facilitate transferring features into the film stack during the subsequent patterning processes. During the patterning process, the circuit design is written onto the photomask by exposing portions of the photoresist to extreme ultraviolet light or ultraviolet light, making the exposed portions soluble in a developing solution. The soluble portion of the resist is then removed, allowing the exposed underlying film stack be etched. The etch process removes the film stack from the photomask at locations where the resist was removed, i.e., the exposed film stack is removed.
With the shrinkage of critical dimensions (CD), present optical lithography is approaching a technological limit at the 45 nanometer (nm) technology node. Next generation lithography (NGL) is expected to replace the conventional optical lithography method, for example, in the 32 nm technology node and beyond. There are several NGL candidates, such as extreme ultraviolet (EUV) lithography (EUVL), electron projection lithography (EPL), ion projection lithography (IPL), nano-imprint, and X-ray lithography. Among these, EUVL is the most likely successor due to the fact that EUVL has most of the properties of optical lithography, which is more mature technology as compared with other NGL methods.
Accordingly, the film stack is being developed to have a new film scheme so as to work with the EUV technology to facilitate forming the photomask with desired features disposed thereon. The film stack may include multiple layers with different materials to be etched to form the desired features. Imprecise etch process control may result in critical dimension (CD) bias, poor critical dimension (CD) uniformity, undesired cross sectional profile and etch critical dimension (CD) linearity and unwanted defects. It is believed that EUV technology may provide good CD uniformity, less etching bias, desired linearity, less line edge roughness, and high thickness uniformity and less defectivity.
In one etch process, known as dry etching, reactive ion etching, or plasma etching, a plasma is used to enhance a chemical reaction and etch the patterned film stack of the photomask. Undesirably, conventional etch processes often exhibit etch bias due to attack on the photoresist material utilized to pattern the film stack. As the photoresist or sidewall of the film stack is attacked during the etching process, the critical dimension of patterned resist is not accurately transferred to the film stack. Thus, conventional etch processes may not produce acceptable results for photomasks having critical dimensions less than about 5 μm. This results in non-uniformity of the etched features of the photomask and correspondingly diminishes the ability to produce features for devices having small critical dimensions using the photomask. As the critical dimensions of photomask continue to shrink, the importance of etch uniformity increases. Thus, an etch process having high etch uniformity to the film stack disposed on the photomask for EUV technology is highly desirable.
Furthermore, high etching selectivity among each layers disposed in the film stack is also desired. As the material layers formed in the film stack may have similar film properties, poor selectivity often occurs while etching each layers disposed in the film stack. Poor etching selectivity may result in poor structure integrity, such as non-uniformity or tapered profile formed on the top and/or sidewall of the formed structure on the substrate, thereby eventually leading to device failure. Therefore, high selectivity of an etching process is increasingly important to preserve profiles and thickness of a photoresist layer while etching an underlying materials in the film stack or the like, disposed underneath the photoresist layer.
Thus, there is a need for an improved etch process for forming a photomask for EUV technology.